XWIKI-17356: Users accounts cannot be enabled/disabled from user profile anymore

  * Extract back velocity code to enable/disable users from the UIXP to
    the actual content of XWikiUserProfileSheet, with some more checks
to ensure of the validity of the request and of the result
  * Check the status of the request in XWikiUserProfileSheet JSX, and
    use appropriate messages in case of problem
  * Call the JSX in XWikiUserProfileSheet UIXP
  * Add missing page object methods for enable/disable button
  * Add a new tests for enable/disable user.